This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-395931, filed Dec. 26, 2000; and No. 2001-376016, filed Dec. 10, 2001, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device for displaying an image using an external light source such as external light entering from an ambient area, or using an internal light source such as a back light in addition to the external light source.
2. Description of the Related Art
Recently, liquid crystal display devices have been used in various types of equipment such as personal computers, RVs, word processors, portable phones, and the like. While the fields in which liquid crystal display devices are applied increase, it is increasingly desired to have a high-performance feature of a compact size, lower power consumption, low manufacturing cost, and the like. In particular, there is a growing demand for the development of a semi-transmission type liquid crystal display device that has both the characteristics of a reflection type liquid crystal display device that has both the characteristics of a reflection type liquid crystal display and those of a transmission type liquid crystal display device as a display device to be applied to portable phones and the like that are used outdoors as well as indoors.
The semi-transmission type liquid crystal display device not only can display an image in the environment of a room, where little external light enters from an ambient area, by optically modulating transmitted light from a backlight through a liquid crystal layer as in a transmission type liquid crystal display device, but also can display an image outside, where a lot of external light enters from the periphery, by reflecting external light by a reflection plate and optically modulating it through the liquid crystal layer as in a reflection type liquid crystal display device. When external light is reflected by a reflection plate in a reflection type or semi-transmission type liquid crystal display device, it is important not to attenuate the intensity of light as far as possible, to display a bright image. In particular, there has been made an attempt to optimally arrange a reflection plate to provide reflection characteristics capable of effectively reflecting external light entering at any angle, as the reflection characteristics thereof greatly affect the attenuation of the intensity of light.
FIG. 17 shows a projection-recess pattern formed in each of pixel electrodes used as a reflection plate in a conventional reflection type liquid crystal display device. The projection-recess pattern includes a plurality of semi-spherical projections irregularly disposed, for example, on the surface of the electrode and a recess surrounding the projections. With this arrangement, the scatter of reflected light is controlled so that the reflected light concentrates in the region of a given range and that the intensity of the reflected light is increased in a particular observing direction.
However, when a single type of projection-recess patterns are formed side by side in the pixel electrodes as shown in FIG. 17, an image of high quality cannot be displayed. That is, the interference of light, which is scattered by the projection-recess patterns of the pixel electrodes, is made regular as a whole. Thus, the interference of light makes it difficult to observe an image. Further, the refraction factor of the liquid crystal material of a liquid crystal layer has a wavelength dependency. Thus, even if white external light is incident on the projection-recess patterns of the pixel electrodes from one direction through the liquid crystal layer, the external light is scattered in different directions with a deviation depending on each wavelength. Accordingly, the color of an image varies with the visual angle of an observer to a display surface. In particular, in a color liquid crystal display device, color oozing is caused thereby and greatly deteriorates the quality of a displayed image.
The inventions provide, in part, a liquid crystal display device capable of obtaining a displayed image of higher quality using external ambient light.
According to the inventions, there is provided a liquid crystal display device comprising:
first and second electrode substrates; a liquid crystal layer held between the first and second electrode substrates and partitioned into a plurality of pixel regions in each of which the alignment of liquid crystal molecules is controlled from the first and second electrode plates; and a reflection plate formed on the first electrode substrate for scattering light entering through the second electrode plate and the liquid crystal layer, wherein the plurality of pixel regions are formed in an approximately matrix manner, and the reflection plate includes types of projection-recess patterns each separated from another of the same type in at least one of the row and column directions of the pixel regions.
In the liquid crystal display device, the reflection plate includes types of projection-recess patterns each separated from another of the same type. That is, since adjacent projection-recess patterns are different from each other in at least one of the row direction and the column direction of the pixel regions, the interference of light that is scattered by these projection-recess patterns can be made irregular as a whole. Therefore, difficulty in the observation of an image due to the interference of light can be reduced without impairing an excellent contrast in the reflection display mode.
Various objects and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.